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TBI running rich*update post 23*fix post45*

I just ran out and "t'eed" my mity vac into the MAP line with the hand held plugged in. Mityvac showed 25"HG at idle and the hanheld read 9( look at the chart I posted) with a voltage of 1.6. The mechanical gauge stayed steady unless I revved and it would drop off and then spike high when the throttle plates snapped shut.

Yes the temp is as you stated.

Only thing left to check is fuel pressure but the problem here is it'll idle forever with no problem. If FP was high wouldn't it finally load up at idle??? Dunno, back at it tomorrow, thanks again for your help.
 
I checked FP today and have 11.5 lbs of fuel pressure... could get the FP to rise by squeezing the flex portion of the return line but it had to be about squashed flat before the pressure gauge would move. 15PSI gauge from autozone. I had to cut into the hardline to install the gauge. When done I took the gauge tee out and installed the splice as I don't trust that little gauge. Is 11.5 (relative to this gauge) too much pressure????

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Tried working with other things today. Verified that the EGR works by pulling vacuum with Mityvac. When the EGR opened the engine sounded suspiciously like it does when pulling away from a stop. Just for kicks I pulled the hose off of the EGR and took it for a test drive. Could tell immedeately problem was gone!!! Had the handheld plugged in and drove about 10 miles at 65mph. BLM's ran about 129 to 131 and the integrator numbers were in the mid to high 130's. Pulled off the highway and reconnected the hose to EGR. Could tell right away the problem was back. Drove about 1 mile with BLM's back down to 108. Disconnected hose and drove back home BLM's running 129 to 131 range.

My guess is that my EGR solenoid is bad allowing vacuum to pass to the EGR?

Don't really understand why this would make the engine run rich but it did.

I'm going to try the EGR solenoid from the '88 "donor truck" and see if it works. I really don't need EGR to pass inspections as we have visual only and I can plug that line internally but I'd rather make it work as GM intended .
 
In the early eighties I was involved in some emission testing at the Transportation Research Center in Ohio. We were getting hydrocarbon spikes on initial pull away from a stop and at steady throttle light load the HC would be high but steady. It turned out to be too much EGR volume under higher vacuum with some load. The excessive EGR was diluting the mixture to the point that it could not sustain the flame front all the way across the combustion chamber and what didn't get burnt was coming out the exhaust as raw hydrocarbons. If I weren't old and senile I might have remembered that before you jogged my memory. Glad you found your problem. BTW, 11.5 pounds is good.
 
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Glad you found the problem. :thumb:
You should fix the EGR instead of unplugging it.. The ECM looks for egr operation. At cruise it cycles the egr open and closed and looks for changes in 02/MAP readings. If it sees no changes it throws a trouble code and backs off timing advance. It wont hurt the engine to run with the egr not working but fuel economy and possibly performance will take a hit.
 
I will fix this properly, but I was thinking... my EGR hhasn't been working properly for 5-6 months now. Shouldn't I have gotten a CEL by now? I'm going to drive it the rest of the week the way it is and tackle the problem this weekend.
 
EGR on MAP looks for a change in manifold vacuum when EGR is commanded, that's how it knows to throw a code or not. I suspect it would still see that change since EGR is only commanded within a narrow range of parameters. (essentially cruise only)
 
More trouble shooting

Continuing to work with this. Yesterday I did get a code 32 while driving with the EGR vacuum line disconnected. I did some trouble shooting this morning and this is what I found. (engine at operating temp)

Probing the EGR solenoid plug with a DVM the EGR gets a command for about 1-2 secs when the throttle is opened quickly then held at a steady state. After 1-2 secs the "command" (ground) goes away.

Reconnecting the electrical I put a vacuum gauge on the output of the EGR solenoid. Opening and holding throttle the vacuum gauge would show vacuum present for about 1-2 seconds then drop off.

Hooked up system and tee'd vacuum gauge between solenoid and EGR. Opening and holding throttle... vacuum to egr went up... and stayed up!!!

At this point I don't know what to make of this. I did a bunch of introweb reading and found some good info. I THINK that my ECM should "pulse" the EGR system and look for MAP changes. If this is true, anybody know what the frequency for the pulse rate is? I'm thinking I could somehow verify the EGR is getting commands at cruise and try to figure out that the system is being commanded correctly, just not responding correctly.

Also, any idea if the '87 EGR is a backpressure dependant device? All the #s on my EGR are long gone.
 
Could the coil be going bad? If your coil is throwing a minimal spark wouldn't your foot automatically press harder on the pedal and force a richer mixture. Corrosion on the dist terminals (and dirt) could both prevent proper coil saturation and bleed off high voltage under load. Also the thermostat may not be regulating the water temp enough. If you place a cardboard baffle over 1 / 3 of the radiator allowing the water temp to be 190, would it lean out correctly. The fuel map in the prom looks at a bunch of data before it makes a decision. If the truck runs better with the baffle either the temp sender is defective or the thermostat is going bad. One thing to remember - the hotter the engine runs, the more thermally efficient it becomes.
 
I thought I saw somewhere on here that the TBI EGR's were backpressure type.

In any case, if your EGR isn't hooked up and you got a code, that is fine.

There may be a routine that the ECM runs to try and test EGR, if it fails X number of times, it throws a code.

I know with the knock sensor, the ECM checks for operation sometime after startup. I don't recall if the EGR is tested the same way, or ONLY looked at for correct operation. EGR only works when the engine is in steady state cruise, it's very unlikely the ECM is pulsing the EGR incorrectly, unless the throttle position sensor is feeding it bad data.

Doesn't sound like the solenoid is working properly to me, but that's a guess at this point.
 
On the drive to work last night I hooked a vac gauge up to the EGR port of the solenoid and put a vac gauge on the dash> During the 11 mile drive the vac gauge dropped to "0" 3 times for a second or so. After the third "drop" the check engine light came on and I had a code 32 displayed. I believe this is what you describe as a test routine. what I saw from this is the solenoid doing what it was told, I just got to figure out if the EGR is doing what it was told.

I'm going to try hooking up an analog meter to the connector for the EGR solenoid and see what the command signal looks like. I've read terms like "pulse wave modulated" to describe it. This may be in reference to a system more sophisticated than mine. I wonder if a "noid light" would work better than a meter for a visual indication???

Here is a link I found that has more info than any other that I have found so far. http://www.asashop.org/autoinc/dec97/egr.htm

I'm trying to understand how the system is supposed to work as opposed to just throwing $ at it trying to fix it. I'd have to say right now the engine is running smoother than it has for a long time and I think this problem has been slowly getting worse for quite a while.

The backpressure thing has me wondering if I have a developing problem in my cat and the increased back pressure causes the EGR to stay "up" longer or farther open than it should. I think this weekend I'll drop the cat and check for anything unusual in the exhaust system.
 
If you've got the tools, the test for plugged exhaust is to tap the gauge into the exhaust (I suppose you could use the O2 bung) and the spec is somewhere around 5PSI+ is a problem with restricted exhaust. The test is out there somewhere, if you can't find it, let me know and I'll check my service manual for the right numbers.

An easy, although not conclusive, test for a sticky EGR is to simply try to move it with your fingers. On a negative backpressure setup, I'm not sure this works though. It should move smoothly though..carbon buildup tends to cause sticking. The same test with the engine running should result in the engine stumbling when you depress it at idle.
 
My egr moves freely with the "finger method" or vac applied. I'm starting to think that all components are working fine I just may have a downstream problem. I'm aware of the sytem backpressure test but nothing beats taking it apart and looking... I'll probably curse myself halfway thru the job but I'm going to fix this thing one way or another.
 
The unknown would be if you've got a restriction PAST the cat. Pretty unlikely without the cat failing and sending chunks back there, but I suppose a baffle in the muffler could get loose or something.
 
I don't know anything about the EGR systems on these trucks, but if the control signal is indeed pulse-width modulated, you will not be able to read it with your average multimeter. Now, if you have an oscilloscope.....
 
I don't believe these setups to be pulse width...could be wrong, but sounds like something later. Our EGR's seem to operate (relatively) the same as the carbed ones, which are on/off.
 
You are correct about using a "sillyscope", however, I just need to verify a steady signal vs a variable signal (PWM) for now. Yesterdays test was inconclusive. On the way to work I monitored the ECM ground going to the EGR. The DVM I chose to use showed that the "resistance" in the circuit varied in an almost proportional manner compared to the throttle position. I thought HA! it is PWM. Wide open throttle the circuit would go open circuit like it should. However on the way home I had a solid signal to gound the whole time driving so something is not right with the test setup or the ECM output. I'm off to autozone to see if I can rig up a noid light and some weatherpak connectors and build a better test rig. I just wish somehow I can get a definitive answer on what the ECM command to the EGR is...but then I wouldn't be having all this fun right?
 
Did you find any GM information specifically about EGR control in the early injected setups? Camaro's would be the same. I'll do a little digging, but I'm not optimistic someone has posted the actual page describing the signal. :)

Looks like you need a thirdgen account to view this, but...
http://www.thirdgen.org/techboard/attachment.php?attachmentid=66746

It states EGR is "ON" or "OFF", talks duty cycle, then that the ECM grounds the circuit.

With a mention of the code needing 48%+ duty cycle to trigger, everything combines to indicate to me that it's not PWM. Of course, I'm no electrical engineer, but it makes sense to me lol.

If you check that link though, it talks about grounding the EGR test lead, so there is some stuff there.

http://coloradok5.com/forums/showpost.php?p=1244664&postcount=1 Just FYI if you haven't seen it, just a collection of links that help with some codes and diagnosis.
 
The fact that the term duty cycle is used indicated to me there is some pulsing going on as in 100% is always on and 48% is on "half" of the time, whatever "time" reference they are using. I have a light setup right now to "read" the signal, I'm off to work. I'll either know more or be more confused... I love this stuff!!!
 
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